1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), more particularly, to a liquid crystal display capable of compensating feed-through voltage.
2. Description of the Prior Art
With a rapid development of monitor types, novelty and colorful monitors with high definition, e.g., liquid crystal displays (LCDs), are indispensable components used in various electronic products such as monitors for notebook computers; personal digital assistants (PDA), digital cameras, and projectors. The demand for the novelty and colorful monitors has increased tremendously.
As the number of pixels increase to improve definition of an active-matrix-type LCD, the following problems have arisen. The number of data signal lines and scan lines have significantly increased along with the number of pixels and the number of driver ICs. This has increased cost and complexity. Many solutions have been proposed to reduce the number of circuit components. For example, an electric potential can be supplied from one data signal line to two or more adjacent pixels in a row. The signal for each pixel is provided in a time-division multiplexed manner to reduce the number of driver ICs. With reference to, for example, U.S. Pat. Publish No. 20050083319A1, U.S. Pat. No. 6,414,665 and U.S. Pat. No. 6,476,787, though, these design can reduce the number of driver ICs by half, but feed-through voltage effect causes voltages applied on two pixel electrodes of a pixel unit are different, thereby reducing display quality.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a circuit diagram showing a pixel unit of the liquid crystal display according to the prior art. FIG. 2 is a timing diagram showing scan signals on the scan lines depicted in FIG. 1. The liquid crystal display 10 contains a gate driver 14, a source driver 16 and a plurality of pixel units 20 arranged in an array. Each pixel unit 20 includes a first pixel An and a second pixel Bn. In a time period T5-T6, the gate driver 14 outputs scan signals on scan lines Gn, Gn+1 at high voltage level to turn on the transistors 11, 12, 21. The source driver 16 sends data signal to the pixel electrodes An and An+1 via the transistors 11 and 21. Meanwhile, the second pixel Bn receives the data signal via the pixel electrode An+1, because the transistor 12 is turned on. In the time period T6-T7, the scan signal on the scan line Gn is at high voltage level to turn on the transistors 11 and 12, while the scan signal on the scan line Gn+1 is at low voltage level to turn off the transistor 21, so that the voltage applied on the pixel electrode An equals to data signal, but the voltage applied on the pixel electrode Bn is not as the same as the data signal due to the reason that the transistor 21 is turned off. Furthermore, while the transistor is turned off, a voltage of the pixel electrode is varied due to parasitic capacitor between the gate and the source of the transistor. That is, at the time T6 which the scan signal on the scan line Gn+1 is varied from the high voltage level to the low voltage level, a voltage drop VfB1 of the pixel electrode Bn results from a parasitic capacitor Cgd2, and the voltage drop VfB1 is named as “feed-through voltage”. Similarly, at the time T7 which the scan signal on the scan line Gn is varied from the high voltage level to the low voltage level, turning on the transistors 11 and 12, feed-through voltages VfB2, VfA of the pixel electrode Bn and the pixel electrode are induced by parasitic capacitors Cgd1, Cgd2 of the transistors 11, 12, as shown in FIG. 3. Then, before the scan signal on the scan line Gn returns to the high level, the source driver 16 will not provide data signal to the pixel electrode An and the pixel electrode Bn. After the time T7, the effect of the feed-through voltages of the pixel electrode An and the pixel electrode Bn remains. Because the feed-through voltage (VfB1+VfB2) of the pixel electrode Bn is greater than the feed-through voltage (VfA) of the pixel electrode An, the grey levels displayed by the pixel electrode An and the pixel electrode Bn are different, accordingly.